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     STDIO(3S)                                               STDIO(3S)

          stdio - standard buffered input/output package

          #include <stdio.h>

          FILE *stdin;
          FILE *stdout;
          FILE *stderr;

          The functions described in Sections 3S constitute an effi-
          cient user-level buffering scheme.  The in-line macros getc
          and putc(3) handle characters quickly.  The higher level
          routines gets, fgets, scanf, fscanf, fread, puts, fputs,
          printf, fprintf, fwrite all use getc and putc; they can be
          freely intermixed.

          A file with associated buffering is called a stream, and is
          declared to be a pointer to a defined type FILE.  Fopen(3)
          creates certain descriptive data for a stream and returns a
          pointer to designate the stream in all further transactions.
          There are three normally open streams with constant pointers
          declared in the include file and associated with the stan-
          dard open files:

          stdin     standard input file
          stdout    standard output file
          stderr    standard error file

          A constant `pointer' NULL (0) designates no stream at all.

          An integer constant EOF (-1) is returned upon end of file or
          error by integer functions that deal with streams.

          Any routine that uses the standard input/output package must
          include the header file <stdio.h> of pertinent macro defini-
          tions.  The functions and constants mentioned in sections
          labeled 3S are declared in the include file and need no fur-
          ther declaration.  The constants, and the following `func-
          tions' are implemented as macros; redeclaration of these
          names is perilous: getc, getchar, putc, putchar, feof,
          ferror, fileno.

          open(2), close(2), read(2), write(2)

          The value EOF is returned uniformly to indicate that a FILE
          pointer has not been initialized with fopen, input (output)

     STDIO(3S)                                               STDIO(3S)

          has been attempted on an output (input) stream, or a FILE
          pointer designates corrupt or otherwise unintelligible FILE

          Buffering of output can prevent output data from being seen
          until long after it is computed - perhaps never, as when an
          abort occurs between buffer filling and flushing.
          Buffering of input can cause a process to consume more input
          than it actually uses.  This can cause trouble across exec
          (2) or system (3) calls.